Primary cultures of hepatocytes on collagen membranes will be used as a model for in vitro studies in chemical hepatocarcinogenesis. The objective is to study the interaction of chemical carcinogens and hepatocytes in terms of repair of DNA damage and neoplastic transformation of hepatocytes. DNA repair will be assessed as unscheduled DNA synthesis, repair of single or double strand DNA breaks and removal of carcinogens bound to the hepatocellular DNA. Correlations between carcinogenicity and patterns of repair of DNA damage elicited by chemical carcinogens will be attempted. The effects of hormones and other biologically active compounds on these processes will be analyzed. Hepatocytes from adult rat livers (normal and preneoplastic) and neonate rat livers will be used. Primary cultures of hepatocytes from adult rat normal and regenerating rat liver will be exposed to chemical carcinogens in order to study the production of "altered" hepatocytes. This process, already shown to occur in vitro with the procarcinogen AAF, will be studied with other chemical carcinogens. The effect of hormones and other biologically active compounds in this process will be analyzed. The neoplastic potential of the altered hepatocytes will be evaluated with in vitro and in vivo techniques (growth in soft agar, formation of tumors in syngeneic animals, etc). These experiments will help understand the factors that determine the outcome of interaction between carcinogens and hepatocytes and the growth of initiated hepatocytes at the early stages of hepatic neoplasia.